Purpose: This study was conducted to evaluate the effect of rein forcement of different concentrations of nano-ZrO 2 and nano-Al 2 O 3 on the flexural strength and impact strength of repaired acrylic resin denture bases. Materials and Methods: A total of 100 specimens were prepared from heat-polymerized acrylic resin and then they were equally divided for the flexural and impact strength tests. 50 specimens were assigned for each testing group. For the flexural strength testing, metallic rectangular molds with rectangular-shaped (65 mm length x10 mm width x 2.5 mm thickness) were prepared. While specimens for the impact strength testing were prepared using rectangular-shaped molds with dimensions of (50 mm length x6mm width x4mm thickness). The prepared intact specimens were cut vertically in two halves along their long axis. For the flexural and impact strength testing, a repair gap was done. Specimens for each strength test were divided into one control group (specimen repaired with autopolymerizing acrylic resin with no fillers) and two repair groups with 2 concentrations (2% and 5%) of nano-ZrO 2 fillers and two repair groups with 2 concentrations (2% and 5%) of nano-Al 2 O 3 fillers. Flexural strength was measured using an Instron mechanical testing machine and impact strength was measured by Izod impact tester. Results: For the flexural strength results, the highest flexural strength was recorded with the 5% nano-ZrO 2 fillers repair group followed by the 2% nanoZrO 2 group which also recorded higher significant mean value than the control group. In both nano-Al 2 O 3 groups, there was a highly significant reduction in the flexural strength for both concentrations. For the impact strength results, the highest impact strength was recorded for the 2% nanoZrO 2 fillers repair group followed by the 5% nano-ZrO 2 group which also recorded higher significant mean values than the control group. In the 2% nano-Al 2 O 3 repair group, there was a non-significant difference in the impact strength mean values compared with the control group. While the repair group reinforced with 5% nano-Al 2 O 3 showed significant reduction in impact strength. Conclusions:The incorpora tion of nano-ZrO 2 into repair resins may improve the flexural and impact strength of the repaired denture base whereas nano-Al 2 O 3 caused reduction of both strengths.

Purpose:The aim of the present study was to evaluate the effect of denture cleansers on the flexural strength, color stability and surface roughness of flexible denture base resin as well as micro wave cured denture base resin. Materials and Methods: A total of 144 specimens were fabricated. Seventy two specimens were constructed from each type of resin and were further subdivided into 3 subgroups (n=24) according to their immersion in different types of denture cleansers. Subgroup1: distilled water (control), subgroup 2: 5% sodium hypochlorite and subgroup 3: effervescent alkaline tablets (Corega tabs). The color changes and surface roughness were measured for each subgroup before (baseline) and after immersion in the solutions. The flexural strength was also measured after their immersion. Results: For both groups (flexible denture base resin and microwave cured denture resin groups); control subgroup showed the statistically significant higher flexural strength values, while subgroup treated with Corega Tabs recorded the statistically significant lowest flexural strength values. Regarding the color changes, for both groups (flexible denture base resin and microwave cured denture resin groups); subgroup treated with Corega Tabs recorded statistically significant highest (ΔE) mean values, followed by subgroup treated with sodium hypochlorite then the control subgroup. However, there was a statistically non-significant difference of the Ra values between the tested groups and subgroups. Conclusions: Within the limitations of the study, it was concluded that the tested denture cleansers had no effect on the surface roughness of flexible and microwave cured acrylic resin, however, significantly influenced their flexural strength. Moreover, denture base polymers are susceptible to color change on immersion in Corega Tabs.

Purpose: In an attempt to improve the mechanical properties, industrially CAD/CAM ceramics blocks have been introduced to dentistry. This study was directed to investigate the influence of the material thickness on the fracture resistance of CAD/CAM Resin Ceramic and CAD/CAM Ceramic and asses the fatigue resistance of class II mesio-occlusal-distal (MOD) inlays of both materials and compare their microtensile bond strength (μTBS) after cementation by two different adhesive resin cements. Materials and Methods: A total of 70 specimens were fabricated. The specimens were divided according to the material used into two main groups (n= 35). Group 1 specimens were fabricated from CAD/CAM Resin Ceramic (Vita Enamic), whereas Group 2 specimens were fabricated from Lithium disilicate glass ceramic (IPS e-max CAD). Specimens of each group were further subdivided into 3 subgroups according to type of testing (microtensile bond strength test, fracture resistance and fatigue resistance tests). Specimens of subgroup of microtensile bond strength test (n=40) were further subdivided into 2 divisions (n=20) according to type of surface treatment (control and sandblasting). Then each division was further subdivided into 2 subdivisions (n=10) according to type of cement used (Rely X Ultimate and multilink N). Furthermore, subgroup of fracture resistance test (n=20) was further divided into 2 division (n=10) according to thickness (0.5 mm and 3 mm). Two-way analysis of variance ANOVA test and three-way analysis of variance ANOVA test of significance were done for comparing variables. Results: For microtensile bond strength, it was found that the highest μ-tensile bond strength value was recorded for Multilink N control subgroup (54.07±7.9 MPa), while the lowest μ-tensile bond strength mean values was for Rely X Ultimate sandblasted subgroup (37.12±2.5 MPa) and IPS e-max CAD. Results revealed that the highest µ-tensile bond strength mean value was recorded for Rely X Ultimate

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Purpose: The purpose of this study was to evaluate the effect of incorporation of different concentrations of hydroxyapatite nanorods into two adhesives of two commercial adhesive systems in order to evaluate the effect on rheological properties, microshear bond strength and degree of conversion. Materials and Methods: One hundred twenty specimens were used in the present study. The specimens were divided into two main groups (n=60) according to the type of commercial adhesive used AdheSE Bond (I) and Tetric-N Bond Universal (II). Then each group was subdivided into 4 subgroups (n=15) according to the concentration of incorporated HAp nanorods 0(control), 0.2, 2, 10wt%HAp nanorods (A, B, C and D, respectively). Each subgroup was further divided into 3 divisions according to the type of test performed (n=5). For rheological properties measurements, a rheometer was used to measure the viscosity and the viscoelastic behavior of the adhesives. For microshear bond strength testing (µSBS), the specimens were tested by using a universal testing machine. The type of failure was determined by using scanning electron microscope. The degree of conversion was measured using Fourier Transform Infrared (FTIR) spectroscopy. The data were analyzed using one-way analysis of variance (ANOVA) and Tukey's post hoc significance difference tests. Differences were considered significant at p≤0.05. Two ways analysis of variance ANOVA test was used to study the statistical significance of the interaction between variables (material and HAp nanorods concentrations). Results: The viscosity of experimental adhesives increased gradually with increasing the concentrations of HAp nanorods. In µSBS test, the AdheSE containing 0.2 and 2wt.% HAp nanorods produced significantly the highest values. Regarding degree of conversion (DC), Tetric-N Bond containing 10wt.% HAp nanorods produced significantly the highest value of DC. Conclusion: Incorporation of HAp nanorods with low concentration (0.2wt %) in AdheSE Bond had a positive impact on the bond strength. However, HAp nanorods as fillers were not suitable to be incorporated in Tetric-N Bond.